The present invention relates generally to agricultural combines. In particular, the present invention relates to a grain cleaning system of an agricultural combine that includes a blower having an adjustable air flow distribution.
Modern combine harvesters can be used for harvesting and threshing a wide range of agricultural products. Combine harvesters include a threshing mechanism where the crop material is threshed in order to separate grains from the discardable part of the crop, and grain cleaning systems where clean grain kernels are separated from other crop particles. In particular, in typical combine harvesters for harvesting crop material, grain is threshed and separated in a threshing and separating mechanism and the separated grain, together with impurities of all sorts, such as chaff, dust, straw particles and tailings, are fed to a cleaning system or mechanism for cleaning. Clean grain is collected below the cleaning system and fed to a grain tank for temporary storage. The tailings are separated from the clean grain and impurities by means of sieves and provisions are taken for recycling the tailings through the combine harvester for reprocessing. This reprocessing involves either recycling the tailings through the threshing and separating mechanism and/or treating them in a separate tailings rethresher means.
Cleaning systems are operated under a wide range of conditions, which sometimes result in a temporary overload of the sieve sections. Cleaning systems in combine harvesters may be temporarily heavily disturbed by local field and crop conditions, such as for instance rapid slope variations or an abrupt increase in crop throughput when the harvester is driven from a low yield spot into a zone with higher yields. Disturbance may also be caused by wrong separation or cleaning settings, difficult cleaning conditions (e.g., from a large amount of green material), or when the threshing settings of the combine harvester are not properly adjusted for harvesting conditions. Such disturbances are known as “transient effects” on the cleaning system and can result in a sudden overload of the cleaning system, e.g., where a heap of crop material accumulates locally on the upper sieve of the cleaning system such that the cleaning system can not fulfill its function. Moreover, a constant overload of the cleaning system ultimately may lead to a substantial rise of the tailings flow ending up with excessive cleaning losses and with blockages of the tailings return system.
Increasing the speed and capacity of the combine is limited by the capacity of the cleaning system to separate the material other than grain (“MOG”) and keep the grain losses within acceptable limits in both flat and hilly conditions. Current technologies provide a partial solution to changes in both incoming crop material quantity and distribution/thickness of crop material on the sieves. Commonly, the operator attempts to reduce sieve losses in such cases by ground speed control strategies, in particular by reducing the ground speed. However, it is not useful to apply ground speed variations once a heap of crop material is present on the upper sieve section because it takes a considerable amount of time to recover from the transient effect such that a significant amount of crop will be lost before the effects of the new speed have stabilized. Furthermore, the sudden increase of sieve losses disturbs the closed loop behavior of automatic grain loss control algorithms and causes serious discomfort to the operator, when operating in automatic ground speed control mode.
Other techniques to address transient effects, especially in hilly conditions, is to respond to crop material thickness variations on top of the sieve by varying the fan speed of a blower of the cleaning shoe. Unfortunately, when increased fan speed and air flow is being used to penetrate the increased thickness of the crop material in the front of the cleaning system based on the slope the air finds the least resistant path which would also effect the air flow and velocity at the rear of the cleaning system leading to unacceptable grain losses, forcing the operator to reduce the harvesting speed in order to limit grain losses.
Thus, a need still exits for a cleaning system capable of addressing the aforementioned defects of current cleaning systems for handling transient effects. Such a need is satisfied by the cleaning system and method of the present invention.